1. Field of the Invention
This invention relates to a hybrid propulsion system for a wheel-driven vehicle with an electric motor, which has two propulsion sources.
2. Description of Prior Art
Auxiliary electrical propulsion systems for vehicles powered by a rider, such as bicycles, tricycles and wheelchairs, have been known for some time.
Propulsion by an auxiliary electric motor is common to all these known vehicles, wherein the motor drives the driven wheel in parallel with the muscle power of the rider. This means that both sources of propulsion act in parallel to provide propulsion, so that their driving torque is added together.
As a result, the two sources of propulsion, the electric motor and the muscle power, act on the same driven wheel. The rpm of the two sources of propulsion are therefore coupled.
An increase in the rpm of the one source of propulsion does not necessarily result in a noticeable increase in the speed of movement. Instead, the other source of propulsion is relieved by this, until at the end its power output drops to zero.
It is possible to remedy this cause superficially by the use of a free-wheeling device, overriding clutches and the like.
It is thus possible to ride, for example, a bicycle with an auxiliary electrical propulsion system at higher speeds than the speed based on the maximum rpm of the motor, without the electric motor acting as a brake. However, it is the nature of the free-wheeling device, or respectively the overriding clutch, that the electric motor no longer provides a propulsive output for movement.
Therefore an increased use of the muscle power of the rider does not cause an appreciable increase in riding speed, but only a relief on the electric motor. With riders who like to move, this leaves an unsatisfied feeling, since they are used to experience an increase in riding speed as a result of an increase in muscle power, even on a non-motorized bicycle.
Frequent shifting is an unpleasant fact for most riders, which reduces the pleasure of riding. By none of the known gear-shifting methods, neither a chain changer nor a hub gearshift, is this unpleasant fact satisfactorily resolved.
Furthermore, in connection with the known electrically driven bicycles it is necessary for the two sources of propulsion, the electrical propulsion system and the muscle power, to operate at the same rotational speed. This means that, for example, an increase in the rotations per minute (rpm) of the electric propulsion system, for increasing the riding speed, is unavoidably connected with an increase in the rpm of the muscle-powered propulsion system. In the case of a bicycle with an auxiliary electric propulsion system this means an increase in the pedaling frequency of the rider. However, ordinary riders are only comfortable within a very narrow range of the pedaling frequency. This range normally lies between 50 and 60 revolutions per minute. It is of course possible to even this out within a defined range by means of known bicycle gearshift devices, for example a chain changer or a hub gearshift. But this means that the rider must operate the gearshift continuously.